1. Field
The present invention relates to an apparatus that converts an interlace-scan video signal to a progressive-scan video signal. More particularly, the invention relates to an apparatus that detects an interlace-scan video signal such as a movie video signal generated in the 2-3 pull-down format or the 2-2 pull-down format.
2. Description of the Related Art
The NTSC video signal generally used as a TV broadcast wave has been generated by performing interlace scanning on an image. The number of equivalent images formed per second is thereby increased, thus reducing a flicker. In recent years, thin TV receivers having a liquid crystal display or a plasma display have come into use in increasing numbers. If an interlace-scan video signal is used in such a display to display the image along the scanning lines, the luminance of the image will decrease so much that the viewer hesitates to see it. Therefore, such a display performs progressive scanning to display images. In order to display an image represented by an interlace signal on a progressive-scan display, an interlace-scan/progressive-scan converting circuit must be used.
The video signals of the standard TV system such as the NTSC system include a video signal generated on the basis of a movie-film image in some cases. A movie-film image is composed of 24 frames per second. On the other hand, a video signal of the standard TV system is an interlace signal representing 30 frames per second (i.e., 60 fields per second). Therefore, the movie-film image is converted to an image of the 2-3 pull-down format or 2-2 pull-down format, obtaining a video signal for the standard TV system. Any interlace-scan video signal obtained by converting a movie-film image to such an image will be hereinafter referred to as pull-down signal.
In the 2-3 pull-down system, for example, a movie film is scanned, generating a progressive-scan video signal having a frame frequency of 24 Hz. Then, the frames of the movie film are converted to fields of a video signal. More specifically, the first frame is converted to the first and second fields (two fields), the second frame to the third to fifth fields (three fields), the third frame to sixth and seventh fields (two fields), the fourth frame to the eighth to tenth fields (three fields), and so forth. Thus, in the 2-3 pull-down system the same image field is repeatedly used, twice or three times. The field signals converted to pull-down signals is reproduced in a format defined by odd-numbered fields and even-numbered fields arranged alternately.
Thus, two frames in the movie film correspond to five fields in a video signal of the standard TV system. In the video signal, two-field parts and three-field parts are alternately arranged, corresponding to the frames of the movie film, respectively.
In order to convert such a pull-down signal to a progressive signal, every two fields generated from the same frame of the movie film must be synthesized into one frame. A video-signal converting apparatus for accomplishing this first determines whether the input video signal is a pull-down signal or not, then determines which fields should be synthesized into a frame if the input signal is a pull-down signal, and finally syntheses the fields, thereby generating a progressive signal. This signal processing is called pull-down interpolation.
To perform pull-down interpolation, it must be first determined whether the input signal is a pull-down signal. Jpn. Pat. Appln. KOKAI Publication No. 2006-20119 and Jpn. Pat. Appln. KOKAI Publication No. 2005-94094 apparatuses for detecting pull-down signals. The apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2006-20119 detects pull-down signals by utilizing an inter-field dynamic/static determination pattern and an inter-frame dynamic/static determination pattern. The apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2005-94094 can discriminate detect pull-down signal even if the pull-down signals are distorted and differs in period.
The conventional apparatus that detect or discriminate pull-down signals is designed on the assumption that the frames constituting a progressive image (24 frames per second), from which a pull-down signal has been generated, are different from one another. In some cases, however, the 2-3 pull-down signal or 2-2 pull-down signal has been generated from a progressive image that is a video signal from which some frames have been extracted and in which the same frame is used twice. Such a video signal is used in animated-cartoon videos.
If a pull-down signal, from which some frames have been extracted, is input, the inter-frame dynamic/static determination pattern will not match with the ordinary pull-down signal pattern. Inevitably, it will take a long time to discriminate the pull-down signal.